Recently, technology for direct transplantation of artificial alternates or cell tissues obtained by culturing cells has been a focus of attention. Typical examples of such technology include artificial skin, artificial blood vessels, and cultured cell tissues. Artificial skin or the like containing a synthetic polymer is not preferable for transplantation because it may cause rejection or other problems. On the other hand, with a cultured cell tissue, there is no concern about rejection, because such tissue is obtained by culturing the cells of a subject into which the tissue will be transplanted and thus it is preferable for transplantation. Such cultured cell tissue is prepared by collecting cells from a subject for transplantation and then culturing the cells.
Many animal cells have adhesion dependency (cells grow while adhering to something). Animal cells are thus unable to survive for a long time period in a floating state ex vivo. In a cell culture for preparing the above cell tissue, for example, a polymer material such as modified polystyrene having enhanced cell adhesiveness through surface treatment or a culture plate that is prepared by uniformly applying a cell adhesive protein (e.g., collagen) or a cell-adhesive polymer (e.g., poly-L-lysine) to glass or a polymer material has been used as a carrier. Cells that have adhered to and grown on such carrier in a planar state grow under a culture environment while forming extracellular matrices comprising proteins and carbohydrates. In general, it is required to harvest such cultured cells through treatment with proteinase such as trypsin or a chemical drug. Thus, such process is problematic in that treatment steps become complicated, the possibility of contamination becomes high, cells are denatured or damaged, original cellular functions may deteriorate, and the like.
Accordingly, JP Patent Publication (Kokai) No. 2003-38170 A discloses a method for producing a cell sheet, which comprises preparing a cell culture support obtained by patterning a temperature-responsive polymer on a culture base, culturing cells on the cell culture support, causing the support to closely adhere to a polymer film by varying temperature, and removing the cells together with the polymer film from the support without damaging the cells, so as to produce a cell sheet.
However, transplantation or the like of such cell sheet obtained by the method disclosed herein into a living body is problematic in that an artificial tissue having a thickness of approximately several hundred microns prepared through multiple lamination of such multiple cell sheets lacks means for transporting nutrients, oxygen, and waste products, and thus it causes cell necrosis within the artificial tissue construct.
It is possible to form an artificial tissue construct with a thickness that does not cause cell necrosis within the tissue, followed by transplantation thereof into a living body, so as to cause angiogenesis to take place in vivo. However, such means is unrealistic, because few cells can be transplanted at a time by such means, and such transplantation should be carried out repeatedly to restore organ functions where there has been damage on a large scale.
Furthermore, a method for constructing an artificial organ using a specific cell culture method is also known (JP Patent Publication (Kokai) 2003-24351 A). With this method, an artificial blood vessel is formed by adhesion of vascular endothelial cells or the like to a tubular cell culture substrate. However, in order to prepare many artificial blood vessels by this method, many finely processed cell culture substrates must be prepared and tissue formation requires much time. Thus, such method has also low industrial productivity.